The field of the disclosure relates generally to gas turbine engines and, more particularly, to a metering valve assembly for a gas turbine engine.
Gas turbine engines, such as turbofans, generally include a fan, a core engine, and a power turbine. The core engine includes at least one compressor, a combustor, and a high-pressure turbine coupled together in a serial flow relationship. More specifically, the compressor and high-pressure turbine are coupled through a rotatable shaft to form a high-pressure rotor assembly. Air entering the combustor is mixed with fuel channeled from a fuel tank and ignited to form a high energy gas stream. The high energy gas stream flows through the high-pressure turbine to rotatably drive the high-pressure turbine such that the shaft rotatably drives the compressor. The gas stream expands as it flows through a power or low-pressure turbine positioned aft of the high-pressure turbine. The low-pressure turbine includes a rotor assembly having a fan coupled to a drive shaft. The low-pressure turbine rotatably drives the fan through the drive shaft. Typically, during gas turbine engine operation, significant heat is produced that raises the temperature of surrounding engine components.
At least some known gas turbine engines use the fuel channeled to the combustor as a coolant for thermal control of the engine components. For example, fuel from the fuel tank is generally at ambient temperature, when the fuel is channeled from the fuel tank to the combustor, the fuel is used as a coolant to extract heat from an engine component. The high temperature fuel is then mixed with compressed air from the compressor and ignited in the combustor to form the high energy gas stream. However, when fuel is subjected to high temperatures, hydrocarbon reactions therein are accelerated resulting in new organic compounds, also known as gum or varnish, that can form and aggregate within fuel system components such as valves. One known solution to reduce the effects of varnish accumulation within the valves is to increase the clearances between valve components. However, increasing the clearance within the at least some valves decrease the valves' operability.